1. Field of the Invention
The present invention relates generally to the field of surface treatment and, more particularly, to methods of producing a water repellent surface on various substrates and to the substrates made thereby.
2. Technical Considerations
Water repellant surface treatments are known in the art. For example, U.S. Pat. Nos. 5,707,740 and 5,980,990 disclose water repellant coating compositions having a perfluoroalkylalkylsilane and an optional integral primer, such as a completely hydrolyzable silane or siloxane. These references also disclose activating the substrate with an acid prior to forming the water repellant coating over the substrate.
U.S. Pat. No. 6,025,025 discloses a method of improving the durability of a water repellant coating on a substrate surface by first applying a dispersion of an abrasive material in an acid solution to expose an increased number of bonding sites on the surface.
Other water repellant coatings are disclosed, for example, in U.S. Pat. Nos. 5,523,161; 5,674,967; 5,328,768; and 5,688,864.
These known compositions and methods provide durable coatings having excellent water repellant properties. Typically, these known water repellant coatings provide contact angles with water on the order of 100xc2x0 or more. Such high water contact angles promote the beading of water droplets on the coated surface. However, high contact angles alone may not directly correlate to how quickly the water beads slide off of the coated surface. As will be appreciated by one skilled in the art, it is desirable that the water beads slide off of the coated surface as quickly as possible. For automotive transparencies, for example, the faster the water beads slide off of the coated transparency the faster acceptable vision through the article can be restored.
One conventional method of characterizing how quickly a water droplet slides off of a substrate is by the conventional xe2x80x9cwater sliding anglexe2x80x9d measurement. The lower the water sliding angle, the faster the water droplets slide off of the surface. Known water repellant coatings typically have water sliding angles on the order of 22xc2x0 or more.
Therefore, it would be desirable to provide water repellant coating compositions and/or coating methods that not only provide commercially acceptable durability, e.g., durability similar to known water repellant coatings, but which also provide lower water sliding angles than known water repellant coatings.
A method of applying a water repellant coating over a substrate surface in accordance with the invention comprises contacting the surface with at least one coating composition comprising at least one perfluoroalkylalkylsilane, at least one integral primer, such as a hydrolyzable silane or siloxane, and at least one substantially non-halogenated, e.g., substantially non-fluorinated, alkylsilane. The method can include contacting the surface with a first coating composition comprising at least one perfluoroalkylalkylsilane and contacting the surface with a second coating composition comprising a substantially non-fluorinated alkylsilane. The first and/or second coating compositions can also include at least one integral primer, such as a hydrolyzable silane or siloxane. Suitable non-fluorinated alkylsilanes include branched or normal alkylsilanes. The non-fluorinated alkylsilane can be selected such that the effective chain length of the non-fluorinated alkylsilane is equal to or longer than the effective chain length of the perfluoroalkylalkylsilane.
A coated article of the invention comprises a substrate having at least one surface and a coating applied over at least a portion of the surface. The coating can be formed from at least one coating composition of the invention comprising at least one substantially non-halogenated, e.g., substantially non-fluorinated, alkylsilane having the general formula R4tSiR5uY4xe2x88x92txe2x88x92u, where R4 can be an alkyl moiety having the general formula CpH2p+1, Y can be a hydrolyzable moiety, such as one or more halogen, acyloxy, and/or alkoxy moieties, and R5 can be an alkyl moiety, such as methyl, ethyl, propyl, butyl, and the like having the general formula CnH2n+1, or a alkenyl moiety having the general formula CnH2nxe2x88x921, such as a vinyl moiety. In one aspect, t can be 1, 2, or 3; u can be 0, 1, or 2; and t+u is less than 4. The coating can comprise the reaction product of (1) the at least one substantially non-halogenated alkyl silane, (2) at least one perfluoroalkylalkylsilane having the general formula (R1R2)mSiR3nX4xe2x88x92mxe2x88x92n, where R1 is a perfluoroalkyl moiety having the general formula CqF2q+1, R2 is a bisubstituted organic radical having the general formula .(CsH2s)., R3 is an alkyl moiety, such as methyl, ethyl, propyl, butyl, and the like, having the general formula CnH2n+1, or a alkenyl moiety having the general formula CnH2nxe2x88x921, such as a vinyl moiety, and X can be one or more hydrolyzable moieties, such as halogen, acyloxy, and/or alkoxy moieties, and (3) at least one integral primer, such as at least one hydrolyzable, e.g., completely hydrolyzable, silane having the general formula SiZ4, and/or such as siloxane having the formula SivOwZ(4vxe2x88x922w). In (3) above for the formula SiZ4 Z can be one or more hydrolyzable groups of halogen, alkoxy, and/or acyloxy moieties. Suitable silanes can be selected from those wherein Z is, for example chloro, bromo, iodo, methoxy, ethoxy and acetoxy. Suitable examples of hydrolyzable silanes include tetrachlorosilane, tetramethoxysilane and tetraacetoxysilane. In (3) above for the formula SivOwZ(4vxe2x88x922w), Z is selected from the group of halogen, alkoxy and acyloxy groups, v is two or more, and w is one or more and (4vxe2x88x922w) is greater than zero. Suitable hydrolyzable siloxanes include hexachlorodisiloxane, octachlorotrisiloxane and higher oligomer chlorosiloxanes. These silanes and siloxanes are further described in U.S. Pat. No. 6,025,025, which is incorporated by reference herein. In one embodiment for (2) above, m can be 1, 2, or 3; n can be 0, 1, or 2; and m+n is less than 4. The water repellant coating can provide the coated article with a water sliding angle of less than 22xc2x0, such as less than 20xc2x0, such as less than 15xc2x0, such as in the range of greater than 0xc2x0 to 15xc2x0.
Another coated article comprises a substrate having at least one surface and a coating applied over at least a portion of the surface. The coating can be formed from a coating composition comprising at least one perfluoroalkylalkylsilane having a first effective chain length and at least one substantially non-halogenated, e.g., substantially non-fluorinated, alkylsilane having a second effective chain length. The second effective chain length can be longer than the first effective chain length. The coating composition can also include at least one integral primer, such as at least one hydrolyzable, e.g., completely hydrolyzable, silane or siloxane.
A coating system, such as a coating kit, of the invention for applying a water repellant coating over a substrate comprises at least one coating composition comprising at least one perfluoroalkylalkylsilane, at least one primer, such as at least one hydrolyzable silane or siloxane, and at least one substantially non-halogenated, e.g., substantially non-fluorinated, alkylsilane. For example, the coating system can comprise a first coating composition comprising at least one perfluoroalkylalkylsilane and a second coating composition comprising at least one substantially non-halogenated, e.g., substantially non-fluorinated, alkylsilane. Either the first or second coating composition can also include an integral primer, such as a hydrolyzable silane or siloxane.